Chemical changes

Question 1

What pH do acids have?

Answer 1

0-6

Red-yellow

Question 2

What pH do alkalines have?

Answer 2

8-14

Blue-purple

Question 3

How can you measure the pH of a solution?

Answer 3

Universal indicator

pH probe attached to pH meter (electronically)

Question 4

acid + base ->

Answer 4

salt + water

Question 5

What are titrations used for?

Answer 5

To find out exactly how what volume of acid is needed to neutralise a measured volume of alkali.

Question 6

What happens when an acid ionises in an aqueous solution?

Answer 6

They produce H+ ions

Question 7

What are strong acids?

Answer 7

Acids that ionise completely in water, eg. sulfuric, hydrochloric and nitrate acids. All of the acid particles dissociate to release H+ ions.

Question 8

What are weak acids?

Answer 8

Acids that don’t fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions.

Question 9

What happens for each decrease of 1 on the pH scale?

Answer 9

The concentration of H+ ions increases by a factor of 10.

Question 10

What is the difference between the strength and concentration of an acid?

Answer 10

acid strength tells you what proportion of the acid molecules ionise in water
acid concentration measures how much acid there is in a certain volume of water

Question 11

acid + metal oxide ->

Answer 11

salt + water

Question 12

acid + metal hydroxide ->

Answer 12

salt + water

Question 13

acid + metal carbonate ->

Answer 13

salt + water + carbon dioxide

Question 14

acid + metal ->

Answer 14

salt + hydrogen

Question 15

metal + water ->

Answer 15

metal hydroxide + hydrogen

Question 16

What is oxidation?

Answer 16

Loss of electrons

Question 17

What is reduction?

Answer 17

Gain of electrons

Question 18

What is a redox reaction?

Answer 18

A reaction where reduction and oxidation are happening at the same time
(REDuction and OXidation)

Question 19

What is an electrolyte?

Answer 19

a molten/dissolved ionic compound which ions pass through in electrolysis

Question 20

Where will positive ions go in electrolysis?

Answer 20

to the cathode (negative electrode)

Question 21

Where will negative ions go in electrolysis?

Answer 21

to the anode (positive electrode)

Question 22

Why can molten and dissolved ionic compounds electrolyse?

Answer 22

they have free ions and can conduct electricity

Question 23

How can metals be extracted? (two ways)

Answer 23

by being reacted with carbon (if it is less reactive than carbon)
through electrolysis (if it is more reactive than carbon)

Question 24

What are the disadvantages of extracting metals by using electrolysis?

Answer 24

method is very expensive

lots of energy is required (to melt the ore and produce the required current)

Question 25

If a metal is electrolysed in an aqueous solution, what will be produced at the cathode?

Answer 25

if H+ ions are present and the metal is more reactive than hydrogen, hydrogen gas is produced
if the metal is less reactive than hydrogen, a solid layer of the pure metal will be produced instead (and this will coat the cathode)

Question 26

If a metal is electrolysed in an aqueous solution, what will be produced at the anode?

Answer 26

if OH- and halide ions are present, molecules of the halide will be formed
if no halide ions are present, the OH- ions (from the water) will be discharged and oxygen gas (and water) will be formed

Question 27

What do half equations show?

Answer 27

the reaction at one of the electrodes in electrolysis